Transverse traveling wave amplifier



July 10, 1951 R. s. BAILEY TRANSVERSE TRAVELING WAVE AMRLIFIER Filed Feb. 4, 194a Patented July 10, 1951 TRAN SVERSE TRAVELING WAVE AMPLIFIER Robert S. Bailey, New York, N. Y., assignor to International Standard Electric Corporation, New York, N. Y., a. corporation of Delaware Application February 4, 1948, Serial No. 6,284

6 Claims.

The present invention relates to a travelling wave amplifier tube and more particularly to that variety of travelling wave amplifier tube in which an electromagnetic Wave exchanges energy 7 with an electronic stream flowing transversely to the direction of propagationof the electromagnetic wave.

Travelling wave amplifiers employing the negative resistance principle are well known in the art. Most of these amplifiers amplify substantially equally well in either direction giving rise to certain disadvantages, especially those of ringing or oscillating. Another disadvantage of the travelling wave amplifier of the prior art is that considerable energy is taken from the incident electromagnetic wave in order to control the motion of electrons which contribute no energy to said wave.

It is an object of the present invention to overcome these difficulties and to provide a travelling wave amplifier in which electrons are injected into the amplification space substantially only at times favorable for energy exchange from the electron stream to the electromagnetic wave.

The method used to obtain amplification in the transverse travelling wave amplifiers of the present invention is to arrange the tube structure in such a way that energy interchanges take place between an electromagnetic travelling wave field and a stream of moving electrons, the greater interchange of this energy being from the electrons to the field. The principle utilised in the present invention is to accelerate electrons by a fixed potential field into a region where they may react with an electromagnetic travelling wave field. It is clear that if any one of such electrons possesses a given kinetic energy corresponding to a given velocity, say Va, and by some agency this Ve is reduced, the kinetic energy of this electron is reduced proportionally to the difference between the squares of the two velocities in question.

By the principle of conservation of energy this energy is imparted to the agency causing the action and thus, if this agency is an electromagnetic wave, the wave will be augmented in energy. The inverse action, increasing electron velocity, results in loss of energy to the electron and is therefore to be avoided.

According to the present invention both the magnetic and electric components of an electromagnetic wave are used to control the direction and velocity of an electron stream in such a way that many of the disadvantages of the travelling wave amplifier of the prior art are eliminated.

It is clear that anelectron remaining in an electromagnetic field for an integral number of cycles of that field will be, in general, unaffected in total energy. An electromagnetic field can be reinforced by a given moving electron only during a half cycle of the electromagnetic wave unless the electron velocity vector is reversed in synchronism with the wave. Thus, amplification of the travelling wave amplifier may occur when an electron is in the field for any integral number of cycles plus /2 cycle. But, in another way, a travelling wave amplifier which produces amplification at a wave length M will also amplify a band of wave lengths up to A1 and then will amplify relatively narrow bands at approximately A, 1 A, 1 5 5 s s The above mentioned and other features of the invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of several embodiments of the invention taken in conjunction with the accompanying drawings wherein:

Figs. 1 and 2 are transverse and longitudinal sections, respectively, of a coaxial line used to illustrate the principles of the invention;

Fig. 3 represents a longitudinal cross section of an embodiment of the invention utilizing a coaxial line;

Figs. 4 and 5 are orthogonal, longitudinal sections of an embodiment of the invention utilizing a wave guide;

Figs. 6 and 7 are transverse and longitudinal sections, respectively, of a second embodiment of the invention utilizing a wave guide.

Referring to Figs. 1 and 2, a coaxial or transverse electromagnetic transmission line is shown together with symbols indicating the direction and polarity of the electric and magnetic vectors in this transmission line. The electric lines are indicated by the solid lines on the drawings while the magnetic lines are indicated by the dotted lines on the drawing. Propagation of the transverse electromagnetic mode requires two conductors l, 2 such as the coaxial transmission line shown in Figs. 1 and 2 or the parallel transmission line well known in the art. This mode-type cannot be propagated in a wave guide and hence is given a separate classification and will be first considered.

The transverse electromagnetic type is characterized by transverse electric and magnetic fields as shown in Figs. 1 and 2, electromagnetic wave will on the average, be decelerated before reach ing the outer conductor, generally held at a high direct current potential. According to the pres= ent invention the magnetic force lines are also utilized to provide focusing and control of emitted electrons from either conductor in order to obtain a higher efi'iciency. I

Referring to Fig. 3 a coaxial trahsverse'el'ectromagnetic mode type is utilized to obtain an amplification according to the principles of the present invention. A coaxial line consisting of an outer conductor 3 and inner conductor 4 and an auxiliary conductor 5 inside conductor 4 and provided with electron emissive electrodes 6 is provided. The openings in conductor 4 are provided with the electron emissive electrodes 6 positioned so that electrons emitted from electrodes 6 will not normally emerge into the space between electrodes 3 and 4. In operation the electromagnetic wave to be amplified is impressed by known means into the coaxial lines consisting of conductors 3 and 4. An auxiliary wave, which may be derived from the main wave, is impressed between the conductors 4 and 5. A fixed direct current potential may be established between electrodes 5' and '4 such that electrons emitted from electrode 6 will be attracted toward 4 but will not, in the absence o'finput electromagnetic waves, emerge into the space between electrodes 3 and 4. However, when the travelling wave amplifiertube is placed in operation and an auxiliary wave energizes the innercoaxial line consisting of conductors 4 and 5, it will be understood that a new force other than the applied static D. C. potential acts upon electrons emitted from electrode 6. This force is due to the magnetic field intensity vector of the incident radio frequency waves and will operate to deflect the electrons into a curvilinear path without altering their velocity due to the static potential between electrodes 4 and 5. Electric field lines due to the main electromagnetic waves between conductors 3 and ti are shown schematically by I. It is seen that these lines reverse in direction-and increase in magnitude periodically each haltwave length.

It is well known to those skilled in the art that the corresponding magnetic intensity line also reverses in direction and magnitude each half wave length. It will then be clear that electrons emitted from electrode 5 due to an auxiliary wave travelling in a direction as shown in the diagram, from left to right, will experience a magnetic force tending to turn the electrons into the gaps in electrode 4 which have been so positioned that electrons from electrode 6 cannot, in the absence of an exciting field, reach the interelectrode space 3', i. However, under the influence of an electromagnetic field travelling in the direction stated, it will be clear that the turning action of the magnetic intensity vector of this field will cause electrons to be deflected thru the opening of electrode 4 and into the interspace between electrodes 3 and 4 of the main. transmission line.-

Between these electrodes is maintained a static D. C. accelerating potential chosen to beef such 6 to the desired temperature.

" transmission line 53.

magnitude that the electronic transit time will be an integral number of half waves of the incident electromagnetic waves plus A; cycle as stated above. understood that amplification will occur in the main transmission line 3, d with a minimum loss of energy; that is no electrons will appear in the space 3, A at times unfavorable for deceleration of the electrons. A pair of conductors 8 is shown for the purpose of heating the emissive electrode It will at once be apparent that an electromagnetic wave travelling in the opposite direction, that is from right to left in the figure, will not be amplified since, due to the reverse direction, all of the electric and magnetic vectors will be reversed and electrons emitted from electrode 6 will impinge on electrode 6 and will not appear in the main transmission line, 3, 4.

In Figs, 4 and 5 a wave guide embodiment of the present invention is shown wherein a main wave guide 9 is provided with a foram'ina'ted electrode it and emissive electrode ll connected to energization means l2. Electric field intensity lines are shown and it is seen that again both the electricand magnetic intensity reverse each half wave along the direction of propagation of electro-magnetic energy in the guide. As in Fig. 3, the electron emissive electrodes H are so. placed with respect to the foraminated structure 10 and the potential difference between the electrodes so adjusted that electrons emitted from H in'the absence of incident radio frequency energy 'all'impinge upon electrode I0 and are there collected, none of them appearing in the main wave guide Operation proceeds generally as recited above. An auxiliary or control wave preferably derived from the main wave to be amplified energizes the wave guide defined by electrodes Ill and i2 while the main wave to be amplified energizes the space l3. Again the magnetic wave vector of the electromagnetic field in the wave guide ii l2 causes the electrons emitted from the electrode H to be turned into a curvilinear path resulting in their emission into the space l3. The wall 9 of the main wave guide is held at a high direct current potential in order to collect electrons emitted into l3. This direct potential is chosen in conjunction with the potential used to accelerate electrons from electrode H to electrode ill and'the electron transit time as described above. It is clear that amplification in the reverse direction, that is from right to left in the figure, will not occur for the same reasons given in connection with Fig. 3.

Referring to Figs. 6 and 7 a waveguide operating in the TE1,l mode is shown provided with means for amplification according to the principles of the present invention. Again electric field lines are shown by solid lines and the magnetic field lines by dotted lines on the figure. The main guide line M is provided with emissive electrodes 55 energized by conductors l6. Accollector plate H is positioned oppositely to the emissive electrode l5 and insulatively but capacitatively connected to the wave guide wall I i. A foraminated structure it is provided in proximity to the electron emissive surfaces l5 and. operated'at a positive direct current potential as indicated at 23. The openings in electrode E8 are again so positioned with respect to electron emissive electrode i5 that electrons can not emerge into the main wave guide transmission space l9 except in the presence of an electromagnetic wave in a predetermined direction down,

Under these conditions it will be the wave guide I 4. Operation proceeds generally as in the preceding cases.

While I have described above the principles of my invention in connection with specific apparatus and with specific electromagnetic mode types in specific transmission lines it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of my invention.

What is claimed:

1. A transverse traveling wave amplifier comprising means defining an electromagnetic wave path and a cathode comprising a plurality of emissive elements mounted adjacent said path to project electrons transversely across said path, an electron focusing means to render said amplifier unidirectional comprising a control electrode mounted between said cathode and said path and provided with apertures and means connected to said control electrode for applying a direct current potential thereto to attract electrons from said cathode, each emissive element of said cathode being disposed in offset relation with respect to an adjacent aperture and said control electrode being coupled to said wave path for applying a portion of said electromagnetic wave between said cathode and said control electrode to deflect electrons through said apertures during one half cycle of the Wave.

2. An amplifier according to claim 1 wherein said cathode comprises a plurality of elements mounted adjacent one edge of the apertures in said control electrode whereby electrons deflected in one direction will pass through said apertures and those deflected in the other direction will K impinge on said control electrode.

3. A transverse travelling wave amplifier comprising an electromagnetic wave path, a cathode mounted adjacent said path to project electrons transversely across said path, a control electrode said coupling being 4 6 said path or in the reverse direction, said cathode including a plurality of electron emissive electrodes mounted in ofiset relation with respect to said apertures so that electrons pass through said apertures only during one half cycle of said wave.

4. A transverse traveling wave amplifier comprising an electromagnetic wave path, a cathode mounted adjacent said path to project electrons transversely across said path, a pair of foraminated electrodes mounted between said cathode and said path and coupled to said wave path for applying an electromagnetic wave therebetween, said coupling being adapted to provide a magnetic component of said wave that will deflect electrons from said cathode in the direction of travel of waves in said path and in the reverse direction, said cathode including a plurality of electron emissive electrodes mounted in spaced relation with respect to said foraminated electrodes such that electrons are deflected through said foraminated apertures only during one half cycle of said wave.

5. An amplifier according to claim 4 wherein said wave path is a coaxial transmission line and said foraminated electrodes are cylindrical and form a coaxial transmission line with one another, the one of said foraminated electrodes adjacent said cathode forming one of the conductors of said first-mentioned transmission line.

6. An amplifier according to claim 1 wherein said wave path comprises a wave guide, said cathode and control electrode being mounted therein, and a collecting electrode is mounted in said wave guide transversely across from said cathode and control electrode.

ROBERT S. BAILEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,122,538 Potter July 5, 1938 2,368,031 Llewellyn Jan. 23, 1945 2,413,309 Beniofi Dec. 31, 1946 

